1. Field of the Invention
The present invention relates to a fastener and a wrapping bag having a fastener of this type capable of being used in wrapping food, drugs, sundries, or the like which must have excellent moisture-proof performance or excellent oxygen resistance, and which must be sealed again after being opened.
2. Description of the Related Art
Bags (zipper bags) of a type which can be freely opened and closed by a band-shaped fastener (engagement member) consisting of male and female elements and disposed at the portion to be opened are widely used in a variety of fields such as food, chemical and sundry fields. A variety of methods have been disclosed in order to manufacture bags having fasteners. For example, a method has been disclosed in which a tubular film, having a fastener constituted by a male element and a female element is integrally extrusion-molded by using an extruding die. Another method has been disclosed in which the fastener is extrusion welded on the surface of a film. Furthermore, a method has been disclosed in which a tape having a fastener is previously manufactured, and the tape thus manufactured is secured on the surface of a base film forming the bag by heat-welding or by using an adhesive.
However, the two former of the three above-described methods encounter problems in terms of difficulty in handling and high cost, for example, the type of resin which can be employed is limited, these methods cannot be easily applied to multilayered film base materials, they are difficult to apply to material of various sizes, printing is difficult, and the like. Therefore, a method based on the latter method has been employed recently, this method being arranged such that only the fasteners are manufactured and they are heat-welded on the surfaces of the films forming the bodies of the bags.
In order to manufacture the fasteners, low density polyethylene (LDPE) is usually used, the LDPE however requiring a high temperature of about 140.degree. C. to be melted and welded. Therefore, it takes an excessively long time to raise the temperature of the portion to be welded. As a result, manufacturing speed must be lowered, causing a problem in terms of low manufacturing efficiency. Furthermore, because of the excessively high welding temperature described above, other problems arise, namely the use of this method results in excessively high energy cost, and wrinkles due to the sealing cannot be prevented, causing the quality of the products to deteriorate. In addition, relatively high rigidity involved sometimes causes a problem in terms of handling depending on the type of articles to be wrapped.
Therefore, it is required that the welding temperature be lowered, bag manufacturing speed be raised, and rigidity be lowered for the purpose of improving manufacturing efficiency, saving energy, and improving the appearance of the products.